Sixteen patients with essential hypertension were treated with N-Amidino-2-(2,6-dichlorophenyl) acetamide hydrochloride (BS 100--141) and clonidine for five weeks each in a double-blind cross-over trial. Dosage ranged from 2 to 6 mg BS 100--141 and from 0.3 to 0.9 mg clonidine daily in two or three divided doses. Both compounds caused a significant and comparable fall in blood pressure. Patients whose blood pressure was not reduced to normal levels by 2 to 3 mg BS 100--141 daily did not respond better to an increase in the dose. Dry mouth and constipation occurred about equally frequently with both agents, but sedation and orthostatic circulatory effects were considerably more frequent with clonidine. Rebound hypertension likewise occurred in five patients following clonidine withdrawal as opposed to no patient after BS 100-141.